He's not a prepared-sound-bite kind of guy, though you might not blame him if he were. Few celebrities have had to lick their wounds as publicly as he has. So his spate of publicity for his new The Singing Detective could have been your standard atonement tour: Celebrity offers gift-wrapped comments about his past troubles and current clean-and-sober state, then gets down to the business of film promotion.

Downey's mind doesn't work that way. It's far more spontaneous, funny, sharp and free-associating - a whirling thingamabob firing on many cylinders at once. So a movie-related conversation veers into an analysis of post-Baby Boomers' global/cosmic responsibilities, which opens the gate for this train of thought:

"I didn't know this until a couple of days ago: Sikhs only have one kid - unless they have twins, in which case they capitulate; they don't get all Spartan about it," the 38-year-old actor said. "They only have one kid because it's a divine responsibility to care for just one human life. I think it's great that (Mel) Gibson has a slew of kids, but there's something to be noted in that principle, you know? There's also something to be noted in maybe not wearing (expletive) white for the rest of your life. And there's something to be noted in wearing white for the rest of your life. It's just a little extreme."

The interview took place in two stages. In part one he was seated at Shaw's Crab House, stripped down to a black tank top, his muscular shoulders each boasting a prominent tattoo: "Indio", the name of his 10-year-old son (by ex-wife Deborah Falconer) on the right; "Susie Q", a tribute to live-in girlfriend Susan Levin, on the left.

The previous night Downey had received the Chicago International Film Festival's career achievement award; there was a presentation ceremony followed by a screening of The Singing Detective, Keith Gordon's movie remake/condensation of Dennis Potter's six-part BBC-TV series about a mystery writer suffering musical hallucinations and depression while hospitalized for a severe case of psoriasis.

The movie went over well, and as Downey enjoyed a perch lunch, he was feeling upbeat. "I'm definitely surprised," he said. "I always suspect what usually happens, which is a lot of effort and then zero payoff." In terms of the movie's quality or reception? "Both," he said. "One feeds the other."

The ensuing conversation was a freewheeling journey into Downey's psyche as he explored his years of unshakable pessimism, desperation and self-destruction - a period he said ended not with his recent return to sobriety or work but his finding a supportive yet stern life partner in Levin, who produced Gothika, in which he has an understated supporting role. In his searing self-analysis, Downey displayed a characteristic that drives his acting: the sense he's being fully honest as he taps into a deep well of emotions with no apparent effort.

"He's very transparent in a way that I think is very endearing, and I think it's part of what's so great about his acting," Gordon said in a phone interview. "He'll play these characters who on the surface may keep people at a distance, and he's so transparent that you see the emotion underneath."

Alas, when the lunchtime conversation reached a natural pause point near the end of the meal, the reporter checked the tape recorder for a second time and found that something resembling Lou Reed's "Metal Machine Music" had taken over, leaving only a few audible minutes before a high-pitched buzzing abruptly drowned out everything. (At first Downey thought the culprit might be his magnetic neck pendant, made from a Chinese alloy meant to fend off radio signals.) No matter. Downey believes everything happens for a reason, so he immediately offered to try again on the phone. About a week later he was spending another hour diving into his past and present with equal fearlessness, though from different angles.

But he prefaced this, his final Singing-related interview, by saying, "This is my last tour de force of the past. In a way I was obliged to (talk about past troubles) because it's kind of my first thing out of the box since being out of the box, really, so there was a certain sense of deformed obligation. But that's it, dude. I'm done."

He spoke while wheeling a "little green chair" around the small Hollywood apartment into which he and Levin were moving. "Everything in this room looks like the kitchen scene from Poltergeist, and it's cool," Downey said. "We're in the middle of this chaotic shift into simplification, and it's really interesting. It doesn't have to be stressful. I think the reason things are different is, you know how some people use external obstacles as a reason to be as miserable as they were going to be anyway? Why not use those obstacles as a reason to be here and just (forget) it?"

Downey is no stranger to raising obstacles to happiness. The young actor developed a dangerous appetite for drugs, even as he was frequently being tagged "best of his generation" and receiving a best actor Oscar nomination for 1992's Chaplin. "My motivation has always been straight-ahead connection, survival, whatever gets you through the night - and the things that were getting me through the night were getting me through the night, but then I was up all night," he said. "So that was a fool's errand I sent myself on thousands and thousands and thousands of times."

Because Downey is one of Hollywood's most widely liked and respected actors, he was able to get work following each setback. But after another relapse during his acclaimed guest stint on Ally McBeal, his sad struggles had become too repetitive to bear, either by the industry, which was loath to insure him, or the once-admiring press, whose coverage had become a collective eye roll. He only got the Singing Detective gig after producer/co-star Gibson visited him in his court-ordered treatment house and lobbied him to take the part. You can see why the role would resonate with a determined-to-stay-straight Downey: His character, Dan Dark, begins the movie debilitated and furious before moving toward physical and emotional recovery.

Downey has said of The Singing Detective: "This is the first film I did from A to Z without getting in my own way." And he wasn't necessarily talking about drugs. "I've done films sober before," he said. "That's not the point. Sober or not sober has nothing to do with getting in your way. As a matter of fact, when I did Home for the Holidays I still believe it's the most relaxed performance in the history of cinema. However, I was loaded."

His much-praised Singing Detective work differed from that on such films as 1987's Less Than Zero and Chaplin, both of which he likened to channeling.

"I bet Chaplin dropped down into me just to make sure I didn't make him look bad," he said. "The difference with Singing Detective is I was revealing myself, essentially. And believe me, it's a lot weirder for me than it would be for anyone who watches it." "Robert's got this amazing ability to transform himself without going through some of the gyrations that I think most actors need to," said Gordon, who co-starred with Downey in 1986's Back to School. "A lot of actors work more intellectually than Robert does, and they break down the part and they talk about it a lot. Robert would do these quantum leaps in working on the character, from going, 'I can't do that' to then coming in the next day and just being there."

But Gordon said one area where Downey struggled was conveying Dark's anger. "Robert by nature is not a very angry person," the director said. "He's very sweet. I said, 'You're going to be lying in a bed unable to move, wearing five pounds of latex, sweating under hot lights. You can either get cranky and whiny with the crew, or you can use all that frustration to find the anger in the guy,' and he went and got it.'"

Now, Downey said, he's been getting in touch with his angry side and has become more likely to trash things than to bottle them up. Since last year Downey also has been studying martial-arts six days a week, though "I'm still routinely getting beat up by blue-belt housewives." He's learning to deal with the well-intentioned but double-edged compliments he routinely gets from fans, who tell him they admire his talent so much that they hope he'll quit squandering it. "I make sure it's not loaded or that there's not a hidden agenda in that statement," he said. "(Otherwise) I let it in, and it feels great and I can work with that for a minute."

He said he's forgiven Woody Allen for dropping him from his next movie over insurance concerns. And he refuses to make excuses for himself, calling the traps he used to set for himself "despicable."

"'And the only person he's hurting is himself,'" he mockingly quotes one of the standard defenses of his behavior. "I mean, Christ, if anyone ever says that within 50 feet of me again, I'm going to make them wish they hadn't supported me at all, in their way, in that limousine liberal 'No one understands addiction. This court system needs to - we need to rehabilitate everybody.' It's like, no, people need to get right, and then they can rehabilitate themselves. And of course you need a lot of [expletive] support, but what kind? And for how long? And with whom? Oftentimes part of the problem is that the troubleshooting guide was written by [expletive] creeps!"

His voice immediately lowered. "Do you know what I mean?"

Now the actor hopes to record his first solo album soon - he said his songs are "like jazz fusion with kind of a Loudon Wainwright thing going on" - and he has been talking with L.A. mover-shaker types about launching some kind of synergistic theater/film/music project. And reports from last week's Detective premiere in London had Downey engaged to Levin.

But in case anyone thinks he has everything figured out, he said they should know this fact:

"I can't handle pets," he said. "If someone gave me a lizard right now, I'd [expletive] nut up. I got a dog out in Malibu that thank God someone's taking care of. I got a snake that my assistant's taking care of. I got both of them for my kid, who's going, 'Where's Tangy? Where's Bonnie? Where's our Rottweiler?' I'm like, 'Trust me, they're where they need to be right now.' Because if I had a dog come and gak on me at 9:30 in the morning, I would probably have to reassess my life mission. Things would go straight Looney Tunes, and I wouldn't be able to explain it until I was out on bail."

So Downey is sticking to at least one simple rule: Move forward; don't look backward. "To most people these are straight rules of thumb," he said. "To me they're like the secrets of the universe revealed."